ECG-based Indices of Physical Activity

This article originally appeared in Computers in Cardiology 1992,
vol. 19, pp. 403-406 (IEEE Computer Society Press). Please
cite this publication when referencing this material. A sample implementation
of the algorithm described in this paper is available in source form
here.

Abstract:

Inter-subject comparisons of heart rate variability (HRV) require
that physical activity levels be matched between subjects, to minimize
the confounding effects of intra-subject variability in HRV
measurements. HRV studies based on standard ECG recordings are
hindered by these effects. The current study investigated methods for
finding periods of minimum physical activity based on the ECG alone.
This paper describes an ``activity index'' (based on mean heart rate,
total power of the observed heart rate signal, and a heart rate
``stationarity index''), and presents an algorithm for locating periods of
minimum activity by tracking this activity index. The algorithm was
tested using a set of 35 ECG recordings for which an independent
activity indicator was available. The algorithm consistently selected
periods of minimum activity in agreement with the independent activity
indicator. No discrepancies were noted in any of the 35 cases.